Postretirement Benefits (Details 2)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee pension plan
Actuarial assumptions used to determine benefit obligations:
Discount rate (as a percent)	4.57%	4.17%	5.11%	4.19%
Compensation increases (as a percent)	3.32%	3.32%	4.15%	4.15%
Actuarial assumptions used to determine net periodic benefit cost:
Discount rate (as a percent)	4.17%	5.11%	4.19%
Expected return on assets (as a percent)	7.00%	7.00%	7.50%	7.50%
Rate of compensation increase (as a percent)	3.32%	4.15%	4.15%
Supplemental employee retirement plan (SERP)
Actuarial assumptions used to determine benefit obligations:
Pre-retirement discount rate (as a percent)	4.57%	4.17%	5.11%	4.19%
Post-retirement discount rate (as a percent)	4.07%	3.67%	4.61%	3.69%
Compensation increases (as a percent)	5.00%	5.00%	6.00%	6.00%
Actuarial assumptions used to determine net periodic benefit cost:
Pre-retirement discount rate (as a percent)	4.17%	5.11%	4.19%
Post-retirement discount rate (as a percent)	3.67%	4.61%	3.69%
Rate of compensation increase (as a percent)	5.00%	6.00%	6.00%